I finally got Buffalo II (ESS9018-based DAC) and SEN up and running a week ago. I managed to arrange things so they interconnect in a close to ideal manner- although they are hard wired together which made assembly, and will make any subsequent upgrades, trickier than usual. I hard wired a Ĺ AVCC supply on to each SEN board - just two 1 % 1k metal film resistors and a 200u Panasonic FM cap. These are fed directly from the output and ground pin of the relevant AVCC regulator (L and R) on the Buffalo board. Apart from the + and Ė signal inputs and outputs, the only other connection to each SEN board is a wire, from the ground plane of the Buffalo, close to the outputs, to the ground sides of the IV resistors. The latter are connected together on each SEN board. I used 330 R, Takman MF 0.25W) IV resistors. (The output level is a bit high for my application, and so I will soon change these for Charcroft 150R types. Though as Patrick points out, 680 R is recommended by ESS, and gives the standard output level.) I used 220 u/ 16 V Nichicon ES bipolar caps (soon to be 470 u) in parallel with 1u Panasonic ECPU types, and 3n3 Panasonic ECHU caps across the IV resistors. (The Panasonics are surface mount types).

I used 16 NiMH AAA 900mAh batteries per supply, recharged from a 24 V switch mode supply. To getting the charging conditions correct, I used series 2 W 22R resistors in parallel with 270 R types, preceded by two suitable Schottky diodes (per supply) to drop the input voltage by 1.1 V to the required value. I used a filter on each supply consisting a parallel 4700 u / 16 V Samwha cap in parallel with a 100 u 16V Panasonic FM, preceded (on the negative rail, as the board layout was more convenient) by a Fastron 10mH choke (77A-103M-00). The DAC board is powered by a mains powered Paul Hynes PR3 series regulator (set to 5.5 V) and all the onboard three legged regulators are suitable Hynes types. I used Tiny XLR connectors wired with Van Damme OFC microphone cable(268ó002ó060) as interconnects

I had delayed construction somewhat, as my (valve) preamp is single ended, and I wanted to avoid using an active BAL to SE converter. To this end I installed 1:1 Jensen JT- P11-1 input transformers in my preamp, terminated wit h the recommended resistor Ėcapacitor network, and directly in front of my (LDR-based) attenuator and line stage . I wired input switching so that both the balanced output from SEN, and the single ended outputs of my tuner and phono stages went through the transformers. As I had hoped, my single ended sources sounded as good, if not better (CMRR improved?) than before. But I became very confused by listening to my IV stageís- Legatoís- balanced outputs compared with its SE outputs. And listening to its balanced out via the Pass B1 buffer stage I had used between Legato and the op amp- based SE converter stage only confused me further! (All fed, remember, into my new Jensen transformers.) All very different, and, often I preferred the SE outputs- much more macrodynamic and full ďbasedĒ when needed. Both balanced outs were perhaps a little more detailed and natural, but the buffer stage didnít seem to improve dynamics. So it was with trepidation that I installed the SEN circuitry....

I did have a slight problem with the latter. A buzz was apparent at high volume settings, despite mains grounding the casework. After a few red herrings I found that touching e.g. the wiring from the batteries and their circuitry stopped the buzzing. I fitted a sheet of thin, adhesive-backed copper sheet to the top of the battery boxes, and the buzz disappeared completely.
The output of my CD transport is galvanically isolated, and its circuitry not earthed, so I thought it best to ground the DAC circuit to mains ground, as- in balanced connection through the transformer- it's not connected to signal ground in the preamp either. Though Iíve since lifted the ground with no audible effect (thoughts anyone?)

The voltage offset on turn was a only a few (~ 3 - 4?) mV, and after about 5 hours operation it was only 0.1 mV L, 0.4 mV R!! You can definitely forget those servos guys

Well thatís about it....

Just teasing. I suppose youíd like to know how it sounds?

Stunning. Itís easily the biggest single step improvement Iíve ever made. To pick out a few things-

The dynamics issue is a thing of the past. Bass is now full, extended and controlled. (I always thought this was feature of just active, voltage gain stages. Another thing I got wrong!)Everything is much more tangible and real. Imagery is much more believable. You can hear all the high frequency harmonics of e.g. solo violin rendered with great accuracy and naturalness. Complex material remains open and it components are easily discernible, without the thickening and distortion often associated with transients and high out levels. Piano sound more natural than ever before, both harmonically and dynamically.

As I said- stunning. And even more so, as, like Nic, I didnít even think this was a bottleneck in my system. Donít prevaricate, get soldering!

My most sincere thanks for your very detailed report of your build.
And I am happy that you seem quite satisfied with the results.

For those who have already had the V18 Evaluation kit, I can only encourage you to start building.
For those who can afford to wait, I can also tell you that our digital expert is looking into our own version of the ES9018 / SEN IV combination.
It will take quite some time, but I guess all good things are worth waiting for.....

2) I presume you have a soundcard or better still an oscilloscope. In that case kindly remove your battery case shield and have the buzz back please. Then measure the output and find out for us what the frequency of the buzz is.

We only ever had oscillation once at 90MHz. The gate stopper (100R) stops that completely. So we want to understand why you got buzz.

I have a scope, but only a 20 MHz analogue type. I tried to scope the output, but couldn't get a good lock- a lot was going on I think, not just oscillation at one frequency. But, at the time, I was anxious just to effect a cure, and get listening again

I'm not using a battery supply for the digital circuitry. The main pre-regulator board (PR3) is mounted on the side panel, on the RH side at the front in the photograph. The mains transformer feeding- a bog standard toroid for now- is located off board, several feet away (no interwinding shield)- which is why you assumed battery supply I suppose. I very rarely mount transformers onboard. The analogue supply batteries are in 16 battery holders of four batteries each, stacked in a line of four piles of four

Perhaps relevant is something I didn't mention. When I first noticed the buzz, I tried powering the digital circuitry, including the pre-regulator, from a 12 dc switch mode supply. The buzz stopped.

I used 3n3 Panasonic ECHU SMD caps for Civ. They are soldered under the board, directly beneath the Riv, so not apparent in the photograph. Iíll probably fit 4n7 when I change the Riv to 150 R (I have some to hand). Long term Iíll try 6n8, and also no caps, as the Jensen transformerís response falls off above 100 kHz anyway. On the other hand, itís located in the preamp some distance away...

Paul, the fact that you kill the buzz with a SMPS leads me to believe that the course is likely to come from the digital supply.
A buzz is normally low frequency, so perhaps 50Hz or 100Hz (mains pickup).
But it seems that you also have some HF stuff (80MHz) pickup up as well.
At least there is now a solution, so there is no real need for you to change anything.

We shall try to repeat your setup to see whether we notice the same problem and thenhow it can be solved.
For me still very strange. As said, I never had any problem at all.